It was an injury he played through at the end of the season.
A bit of Terrence Ross news from over the weekend:
Terrence Ross underwent surgery yesterday to remove bone spurs from his left ankle. He played through the ankle injury late in the season
— Josh Lewenberg (@JLew1050) May 23, 2015
Ross had an underwhelming season this year, and didn't show the development some expected after the potential he showed in his first two seasons in Toronto. He is eligible for an extension this summer, but it might be beneficial for both sides to wait until next summer when Ross becomes a restricted free agent to decide on whether there's a long term future here in Toronto.